Adding code to head section: HiFi plugin and WP 3.1.3

Hi!

I need to add code to head section of only one post/page at a time. – I know about the header.php file, but I don’t think I should use it for this since I don’t need to add the code for the whole site. I have installed the HiFi plugin and tried it many times but things are not showing up correctly (a hotel booking form). I see that perhaps HiFI is not compatible with my version of WP – has anyone used it with WP 3.1.3?

Any suggestions of what else I could try? Haven’t found another plugin doing exactly this for one page/post at a time…

Thanks very much beforehand!